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I'm sure many of you have thought about putting LED's in your side markers, but didn't want to give up the benefits of the incompatible blinker mod. Or maybe you upgraded, but miss the way the blinker mod worked. LED's are directional by default, they will only light when current goes though them one direction, which is counter to the blinker mod's reliance on the incandescent bulbs not caring which way current goes.

Sadly, my source for bi-directional BA9s LED's has discontinued their units, and after scouring the internet ever since, there are no other units built that are compatible with the blinker mod. So, what's a guy to do?

It yourself. DIY a circuit to allow current both ways on input, while always sending output one way only. Traditionally this has been done via a diode bridge, which is inherently limited by design -- the current always goes through two diodes, dropping voltage by around 2V while simultaneously limiting current to around 1A (assuming a 1N00... guy is used, which is incredibly common). After research, there is not only a chip designed to do this with minimal extra parts, but it is extremely efficient compared to previous approaches. Behold, the LT4320-1!

It only requires four MOSFET's and two capacitors, and built with the MOSFET's I've selected, appear to allow 10A at something like 100mV drop. This means that you could potentially use this with far more powerful equipment than a simple LED (bear in mind, the incandescent BA9s bulb uses less than 0.5A, LED's are far more efficient!)

Now here's the catch: with one-car quantities, the LT4320-1 itself costs $9.12, however this drops to $6.10 if a quantity of 25 to 99 is purchased, and drops again at 100 units per order. The other components have savings too, but not quite as drastic.

In order to get that lower price, I would need at least SIX individuals to express serious interest. Once they are built, I can start selling them. I have already ordered enough for four boards for my own car as a "test run". Price for that guy is about $15 to $20 per board (I will get a complete rundown once I've finished the board design itself), however with the batch buy, I am suspecting $15 per board may be overall cost. This would mean $90 (plus shipping) per car, assuming four per car.

So the question becomes: how many of you guys are willing to plop $100 on a set of boards that let you pick whatever damn LED you want in the side markers?

(Note: for those of you also interested in my completely-rebuilt side marker project, I will allow returns of the LT4320-1 boards for a full refund up to whatever quantity of side markers you purchase later, as a "Thank you" for early support! So if you buy 8 LT4320-1 boards now, and 4 side markers later, I will refund four of the LT4320-1 on a functional return. Buy four more side markers, I'll refund the final four LT4320-1 boards in your inventory. Simple stuff!)

I'm always concerned about voltage drop with LED power. But I used diodes only dropping 0.2 volts with LED loads. But if you want zero drop, just provide constant 12 volt to the + side of the lights. That is how my car is wired. I did not think of getting light power using diodes when I prototyped these a few years ago.

I will probably increase the price someday. I kept it at $30 just to get enough sold to break even.

I'm always concerned about voltage drop with LED power. But I used diodes only dropping 0.2 volts with LED loads. But if you want zero drop, just provide constant 12 volt to the + side of the lights. That is how my car is wired. I did not think of getting light power using diodes when I prototyped these a few years ago.

I will probably increase the price someday. I kept it at $30 just to get enough sold to break even.

I think mine's somewhere in between there. I mated the LT4320-1 with 3 mOhm MOSFET's. The LT4320-1's datasheet seems to suggest the IC's voltage drop is 55mV, and the MOSFET's voltage drop is (mOhm * A), for an overall formula of:

Your numbers are correct but you don't need to be using those high current samples. I fight with those numbers with my fan relay and fan fail units because the OEM cooling fans can draw 30 to 40 amps for both. You care about voltage drop because voltage times current equal the heat (watts) the parts produce and have to dissipate.

Typical side marker LED current is 30 to 60 ma. for each marker. Even incandescent bulbs are less than one amp.